Various platinum containing catalysts used in a wide variety of hydrocarbon conversion processes are known. Activity of these catalysts gradually declines due to the build-up of coke, until eventually they require regenerating and reactivating. The known methods for treatment of such spent catalyst invariably comprise removal of deposited coke. Typically, the coke is removed by controlled burning in the presence of diluted air at 450° C. to 550° C. High temperatures used for coke removal however lead to agglomeration of the metal particles during processing which in turn affects the textural properties of the catalyst support. This reduces the activity and stability of the catalyst.
Various attempts have been made to overcome the above mentioned shortcomings. A process for the regeneration of a coked catalyst comprising metals from Group IV, VII or VIII of the Periodic Table is disclosed in U.S. Pat. No. 5,183,789. It involves the treatment of the catalyst with a gaseous stream of ozone in air with specific velocity at temperature ranging from about 60° C. to about 120° C.
Another process for regenerating a dehydrogenation catalyst comprising Pt, Rh, Ir, Pd, Ru, and Os deposited on a solid support of porous alumina and an activator component selected from transition metals from periodic table of elements which is specifically used for dehydrogenating (C9-C15) hydrocarbon is disclosed in U.S. Pat. No. 6,700,028. The method step of regenerating the catalyst in accordance with the process disclosed in U.S. Pat. No. 6,700,028 involves heating the catalyst in an oxygen-bearing atmosphere to a temperature sufficient to cause at least a portion of any coke present on the surface of said catalyst to be oxidized. Thus, the scope of the treatment of the catalyst in accordance with the process disclosed in U.S. Pat. No. 6,700,028 is particularly limited to heating in the presence of oxygen bearing atmosphere (O2+N2).
There is also disclosed a process for reactivating a coked and agglomerated platinum-iridium-selenium on alumina reforming catalyst in U.S. Pat. No. 4,492,767. It comprises partial decoking in O2-containing atmosphere at a temperature below about 430° C. followed by reduction of the catalyst using hydrogen gas. The catalyst is then further treated in oxygen free atmosphere with a halide providing compound. This is followed by the method step of re-dispersing the metallic Ir by treating the catalyst with hydrogen and water vapor.
U.S. Pat. No. 6,348,144 provides still another process which involves regeneration of a catalyst comprising Pt on a support like alumina. It comprises a method step of pre-combusting oxygen (air) and a halogen containing compound (e.g. trichloro methane) and withdrawing effluent stream of O2 and halogen. The withdrawn effluent stream is contacted with the catalyst and a portion of the platinum present on the catalytic particles is dispersed.
A method for regenerating a deactivated hydrocarbon conversion catalyst such as dehydrogenation catalyst comprising a combination of a platinum group component, a rhenium component, and a halogen component with an alumina carrier material is disclosed in GB 1293632. It involves contacting the deactivated catalyst with a first gaseous mixture consisting essentially of from O2, H2O, halogen or a halogen-containing compound, and an inert gas (such as nitrogen, helium or CO2), at 375-500° C. This is followed by contacting the catalyst with a second gaseous stream comprising O2, water, a halogen-containing compound, and an inert gas. Subsequently, the oxygen and water in contact with the catalyst are purged using an inert gas. Finally, the catalyst is treated with substantially water-free hydrogen steam at a temperature of from 400 to 600° C. to obtain the regenerated catalyst.
Apart from the above patent documents, methods for regenerating alumina supported polyatomic catalysts Pt—Sn/Al2O3, PtReSn/Al2O3 and PtReGe/Al2O3 by treatment with oxygen and ozone have been disclosed by Pieck et al and D'Ippolito et al in Applied Catalysis A: General 278 (2005) 173-180 and Applied Catalysis A: General 388 (2010) 272-277 respectively.